cell failure plays a key role in the pathogenesis of type 2 diabetes. Targeted mutagenesis in mice has suggested that altered function of the cell's insulin signaling pathway partly contributes to this defect. In studies supported by this grant, the PI's laboratory has shown that: (i) cell compensation to insulin resistance occurs primarily via increased cell replication; (ii) decreased cell function (insulin secretion) can be compensated for by increased proliferation and vice versa, but (iii) any abnormality of the mechanism coupling insulin secretion with proliferation will shorten cell life and accelerate cell failure. Moreover, (iv) the PI has defined a pathway, comprised of the transcription factors Foxo1 and Pml and of the histone deacetylase Sirt1, that protects cells against hyperglycemia-induced glucose toxicity through the induction of metabolic diapause. Finally, (v) the PI has shown that conditional Foxo1 ablation in pancreatic progenitor cells, but not in terminally differentiated cells, gives rise to numerous insulin-positive cells in pancreatic ducts. Based on these accomplishments, as well as unpublished preliminary data, the PI proposes that a moderate reduction of metabolic activity and sparing use of cell replication are conducive to preserving cell function in the metabolic syndrome. The PI seeks continuing support to investigate critical aspects of this hypothesis, including: (Aim 1) does induction of premature senescence protect against cell failure? (Aim 2) is the decision between cell life (premature senescence) and death (apoptosis) dependent on Foxo1 transcriptional vs. coregulatory functions? (Aim 3) does Foxo1 fine-tune glycolysis via the ChREBP/Nif3l1 pathway? (Aim 4) Can -like endocrine cells be isolated from pancreatic ducts of flPdx-Foxo1 knockout mice? To achieve these goals, the PI proposes studies in which signaling pathways linking insulin secretion to cell proliferation will be altered by gene targeting, and their effects on cell performance studied in various models of type 2 diabetes. The mainstay of this proposal rests on the PI's longstanding experience in introducing mutations in mice and analyzing the consequences by extensive metabolic phenotyping. PUBLIC HEALTH RELEVANCE: Prevention of cell dysfunction is a critical goal of diabetes treatment. Studies supported by this grant have defined mechanisms that we believe to be new, linking insulin secretion with cell differentiation, proliferation and hyperplasia, as well as new biochemical and molecular circuitries that can be exploited for cell replacement in diabetes. These studies have delineated a role for the forkhead protein Foxo1 as a biochemical linchpin among diverse cell functions. We envision that the molecular signature imparted by Foxo1 activation illustrates the concerted regulation of cell function one ought to achieve to prevent cell failure. Thus, the studies outlined in this proposal, while building on the lessons of the past funding cycle, aim to explore the contribution of the identified pathways to the cell's metabolic adaptation in type 2 diabetes. The driving theme of the proposed work is to define cellular pathways that can be enlisted in the clinic against cell dysfunction.